Bodily cancers are commonly treated using radiation therapy. Radiation therapy employs high energy radiation to kill cancer cells. One type of radiation therapy is brachytherapy, in which a source of radiation is in direct contact with an afflicted tissue. A common brachytherapy treatment, transperineal seed implantation, involves placing radioactive seeds in the prostate gland to kill prostate gland cancer cells. A physician employs tools, for example, ultrasound, computed axial tomography (“CAT” or “CT”) scans, magnetic resonance imaging (“MRI”) scans and X-ray images in concert with dose-planning computer software programs to evaluate the medical condition of a patient. The physician constructs an optimal treatment plan to evenly distribute radiation throughout the afflicted tissue. Radioactive seeds of discrete radioactive strengths are inserted into the afflicted tissue through multiple implantation needles at positions corresponding to the treatment plan.
During prostate brachytherapy, the position of the radioactive seeds in relation to the prostate gland and to adjacent structures in the body must be known to a relatively high degree of precision to accurately determine if the dose of radiation delivered from the seeds is adequate to eradicate the prostate cancer. Currently, seeds are guided into the prostate using transrectal ultrasound guidance which is good for imaging the soft tissue of the prostate and the surrounding structures. Occasionally fluoroscopy is used in conjunction with the ultrasound to provide improved images of the seeds. Following the implant, the seed position is typically determined using CT imaging. Using the determined seed positions, the dosimetry of the implant is calculated based on the obtained CT images. The CT images have been shown however to be deficit in imaging soft tissue structures, therefore, performing ultrasound imaging or MRI imaging and fusing the ultrasound or MRI images with the CT images is often performed.
Many of the current modalities have shortcomings that need to be overcome before an accurate determination of implant location can be made. For example, ultrasound can determine the structure of the gland and surrounding anatomy to a high degree of accuracy. However, ultrasound is not very accurate at imaging the seeds. Various attempts have been made to design the seeds to be more echogenic (i.e., more accurately imaged by ultrasound). The brachytherapy seed sold as ONCOSEED™ (e.g., Iodine-125 brachytherapy seed) by Oncura uses ribs on an outer titanium hull of the seed to increase its ultrasonic reflection. Other attempts have been made to incorporate gas bubbles into the walls of the seeds or into stranding material holding the seeds together to enhance the ultrasound reflection. These attempts have been minimally successful primarily due to the small target size of the seed, the background noise caused by the other seeds in the implant, the echogenic needle tracks created in the gland and the like.
Other methods for locating and imaging the seeds also have shortcomings. Fluoroscopy is very good at identifying the seeds due to the heavy metal X-ray markers in the seeds. Unfortunately, fluoroscopy is poor at imaging the soft tissue in and around the prostate gland. CT imaging is acceptable at imaging both the seeds and the soft tissues, but it is far from ideal. CT imaging is typically not refined enough to image critical structures around the gland and therefore, generally used for gross position analysis only. CT imaging is most often used to do post implant dosimetry. Studies have shown that there is a great deal of operator-to-operator variability, however, in contouring the prostate shape and size for a given image. This variability leads to subsequent variations in the determination of the adequacy of the dose delivered.
MRI imaging is the preferred method for imaging the prostate anatomy. Identification of critical structures located around the prostate gland can be performed using MRI imaging. MRI imaging is however rather poor at imaging the seed positions following an implant. Uncontrolled artifacts for the seed can also distort the gland image and make accurate dosimetry assessment difficult. In the presence of sufficient artifacts, the seeds may be invisible to MRI imaging. Additionally, the degree of artifact, or visibility, for a given seed type varies from vendor to vendor and, possibly, even from lot to lot from the same vendor.
Medical professionals therefore are required to compensate for deficits in one or more of the available imaging technologies by employing multiple imaging techniques and fusing the resulting images to determine an accurate location of the implant.
Thus, a need exists for a radioactive seed conducive to providing high fidelity during a magnetic resonance imaging procedure while reducing artifacts caused by the seed in the image.